1. Field of the Invention
This invention relates to a semiconductor device and a manufacturing method thereof and, more particularly, to a semiconductor device comprising a MEMS (Micro Electro Mechanical Systems) device and a manufacturing method thereof.
2. Description of the Related Art
Recently, development of the Micromachine technology has proceeded. As one of techniques of the Micromachine technology, MEMS technique is known. The MEMS technique is a technique of finely producing a movable three-dimensional structure with the semiconductor processing technology.
As devices formed with the MEMS technique (called MEMS devices), variable capacitor, switch, acceleration sensor, pressure sensor, RF (radio frequency) filter, gyroscope, mirror device and the like are mainly studied and developed.
A variable capacitor using an actuator will be explained below. An actuator is a device capable of converting various kinds of energies such as electric energy, chemical energy and the like into dynamically kinetic energy to do a mechanical work.
When a variable capacitor is formed, an upper electrode and a lower electrode which the variable capacitor comprises need to be separated in a few μm. Thus, a cavity having a depth of a few μm needs to be formed in a part of a variable capacitor formation area and a lower electrode needs to be formed under the cavity.
The formation of the cavity needs, for example, steps of depositing an insulation layer having a thickness of a few μm, etching to form a groove having a depth of a few μm in the insulation layer, and depositing a sacrificial layer in the groove. For this reason, longer time is spent in the manufacturing process and the throughput is thereby degraded. Moreover, since the groove is not used for the process of forming a CMOS (Complementary Metal Oxide Semiconductor), mixed mounting of a CMOS is difficult.
As an associated technique of this kind, a piezoelectric MEMS element which functions as a variable capacitor has been disclosed (see U.S. Pat. No. 6,359,374 and U.S. Pat. No. 6,377,438).